During the 1980's and early 1990's, increased awareness of the HIV and hepatitis propagation potential resulting from use of unpurified blood and blood products hampered the development of safe and effective human fibrinogen-based hemostatic dressings. However, subsequent developments on recombinant fibrinogen and recombinant blood factors, as well as on improvements in plasma purification methods, started reversing that trend.
The preferred embodiment of the present invention includes fibrinogen and/or other blood clotting species in a molecular-scale coating on individual fibers of the dressing. The term “molecular-scale coating” refers to a coating with a thickness equivalent from one to about several molecular layers. A typical molecule in blood clotting species is human fibrinogen, which is a protein with a molecular weight of approximately 341,000, and with an oblong shape and a characteristic maximum length of approximately 47 nanometers.
Prior art inclusion of fibrinogen or other blood clotting species in a dressing are typically in multilayered a structure of a distinct layer of blood clotting species, which is, generally evident to the naked eye, and not in a molecular-scale coating which cannot be discerned with the naked eye. The surface of each such distinct layer exposes the blood clotting species to blood and surrounding air. Each such distinct layer has a characteristic length, such as thickness and grain size, that is larger than the average fiber diameter and the thickness of the coating of blood clotting species on any fibers in the present invention. Coatings referred to in the prior art refer to a distinctly different layered coating on the dressing. Unlike the present invention, a prior art coating of active components does not refer to a well mixed coating on the bulk of the fibers in the dressing. Prior art layers are distinctly different and much less efficient than a molecular-scale coating on individual fibers enabled by the method of the present invention.
U.S. Pat. No. 6,056,970 to K. E. Greenawalt, et al. is an improvement over layered dressings. Greenawalt teaches a fibrous dressing wherein the coagulation protein is dispersed throughout the hemostatic composition, but not in a molecular-scale coating on the bulk of the fibers in the dressing. Rather Greenawalt discloses dispersal within the fibers in a manner that captures comparatively larger domains of the protein within the fiber structure. Greenawalt also teaches compressing the fibers into a paper-like compositions so as to prevent activation of fibrinogen during processing. The present invention is an improvement in that the protein is captured in a fiber or as a molecular-scale coating on individual fibers, such that it significantly increases the surface area of exposure of coagulation protein to the blood.
Methods of electrospinning fibers for dressings that contain coagulation proteins are well known. For example, United States Patent Application Publication No. 20060013863 A1 to S. W. Shalaby, et al. published on Jan. 19, 2006 describes such methods and the formation of hemostatic, compliant, elastomeric, multicomponent, fibrous dressings. This prior art, however, but does not teach molecular-scale coatings on the fibers such that a coagulum is formed when exposed to blood.
There are a number of synthetic agents that can potentially improve the performance of fibrinogen-based hemostatic bandages, besides natural ones such as thrombin and other blood coagulation factors. Very recently, the use of propyl gallate and other gallate derivatives has been disclosed to increase the performance of fibrinogen-based hemostatic dressings with hemostatic dressing backings made, among other things, of collagen. U.S. Pat. No. 6,891,077 (2005) to S. W. Rothwell, et al., is an example disclosing this use. Propyl gallate is used in the food industry as an antioxidant additive for oils and fats. The invention offers the capability of incorporating pro-coagulation species, either of natural or synthetic origin, into a fibrinogen hemostatic dressing on a molecular-scale and this is a desirable improvement.
The preferred embodiment of the present invention newly creates the option of occluding propyl gallate and its derivatives within the fibers of the dressing. The Rothwell patent teaches a method of adding a solution of propyl gallate to a bandage, but does not teach using propyl gallate dispersed on a molecular-scale throughout the bandage. The preferred embodiment of the present invention eliminates a cumbersome step of soaking a bandage with aqueous-organic media of non-protein constituents, which in itself is counterproductive because it adds moisture that potentially interferes with formation of a blood clot. Rather, in the preferred embodiment of the present invention, the aqueous-organic media of non-protein constituents is thoroughly mixed part of the solution that is used to make the fibers.
The United States Army has recently used a fibrinogen bandage with a chitosan backing in the battlefield. Besides chitosan, which is a biopolymer derived from the chitin in crustaceans, other polymers such as, but not limited to, polylactic acid, or PLA, and polylactic-co-glycolic acid, or PLGA, may be viewed as good backing materials for a fibrinogen-containing wound dressing. PLA and PLGA degrade in vivo by hydrolysis (esterase activity) into lactic acid and glycolic acid, respectively, which are then incorporated into the tricarboxylic acid metabolic cycle. Besides PLA and PLGA, other bioabsorbable polymers such as, but not limited to, polycaprolactone, and copolymers resulting from combinations thereof, may be used as backing materials for hemostatic dressings. The present invention avoids the use of backing materials or layers and offers the potential to incorporate these polymers directly in or on the fibers of the dressing, creating a high contact surface area promoting rapid blood coagulation.
Fibrinogen has been recently processed into fibers by technique known as electrospinning from 1,1,1,3,3,3-hexafluoroisopropanol solutions. Besides being soluble in water, proteins are often soluble in perfluorinated alcohols such as 1,1,1,3,3,3-hexafluoroisopropanol, and 2,2,2-trifluoropropanol. The acute toxicity of 1,1,1,3,3,3-hexafluoroisopropanol, however, is well documented. Despite the acute toxicity problems, a number of patent applications still describe methods for direct electrospinning of protein solutions in organic solvents for making hemostatic and wound dressings. For example, two of these include United States Patent Application Publication Nos. 2004-0037813 A1 for electrospun collagen and 2004-0229333 A1 for electroprocessed fibrin.
Without the aid of additives that may compromise preservation of the native state of a dissolved protein, or may compromise the intended biological function, electrospinning of aqueous protein solutions, exemplified by PCT application WO/1998/003267 by R. A. Coffee, is generally difficult. Electrospinning a bandage directly on a wound had an initial appeal of making the fibers directly off blood coagulation proteins, avoiding a fibrous backing. However, practical problems in using this approach in situations involving arterial bleeding are that it is time consuming and requires a level of skill not often present. For direct application by electrospinning of aqueous protein solutions to wounds, two additional problems became evident: this electrospinning approach uses a lot more protein than by just coating biocompatible polymer fibers, such as those made from polylactic acid; and, electrospinning of proteins in fluorinated hydrocarbons is cell-toxic if even a trace fluorinated hydrocarbon remains in the fibers.
Electrospinning is used in an embodiment of present invention to create the fibers. This is optionally followed by a drying step to ensure that the solvent is completely gone. The fibers are then coated with one or more blood coagulation proteins. The coating is made from an aqueous solution of the protein to form a molecular-scale coating on fibers of the dressing. This is optionally followed by removal of water from the coating, and optionally a subsequent electrostatic deposition of other proteins of the clotting cascade from dry powders or from aqueous and mixed aqueous-organic media at sub-zero degrees Celsius. This methodology avoids problems with electrospinning poorly biocompatible additives, avoids the unnecessary use of expensive proteins and avoids toxicity altogether. Additionally, the present invention does not make a dressing or bandage when needed at the emergency situation. Rather it is suited only for making the dressing in a manufacturing facility, packaging it, and shipping it for later use.
Accordingly, there is a need for a fibrous hemostatic dressing that improves utilization of blood clotting species via dispersing these species within the fibers of the dressing, or onto the surface of fibers as coatings with thickness comparable in size to the average diameter of the fibers. Thus, the method of the invention delivers a fibrous dressing wherein the individual fibers are coated with blood clotting species that will maximally expose, on first contact with blood, the blood clotting species. The dressing, to with a bandage, would speedily supply active ingredients to the wound in quantities that are not available in the blood coming out of the wound to seal the wound quickly. A dressing made in accordance with the invention does not change the chemistry of the clotting process, but rather delivers blood clotting species at a much higher rate than current dressings. The high surface area of contact of the actives with blood from the wound is what drives a fast clot formation process, while avoiding the use of a large mass of expensive coagulation proteins. In addition, optional biological clot-aiding constituents would improve the natural clotting process by making platelets aggregate at the wound.